To meet consumer demand for a variety of multifunctional electronic devices, such as microelectronic devices, medical devices, wearable electrical materials, and the like, the development of power sources such as smaller, thinner, lighter, and environmentally friendly supercapacitors or batteries has received much attention.
Among such power sources, supercapacitors use a charge phenomenon by movement of ions to the interface between an electrode and an electrolyte or a surface chemical reaction unlike batteries using a chemical reaction, and thus have higher charge/discharge efficiency and longer lifespans than those of batteries. Therefore, such supercapacitors have drawn great attention as a next-generation energy storage apparatus. Of these supercapacitors, micro-supercapacitors (micro-electromechanical systems) use nano- or micro-structured materials instead of large-scale materials, and thus have a large surface area per volume, resulting in easy access of an electrolyte. Thus, various studies into use thereof as a portable and lightweight power source which may be applied to small electronic devices, such as small robots, wearable electronic fabrics, implantable medical devices, and the like, have been conducted.
Recently, a variety of micro-supercapacitors having increased energy and power density have been developed through effective structural design or various preparation methods of various active materials, such as carbon nanotubes, reduced graphene oxides, activated carbon, conductive polymers, and metal oxides. For example, a twist-spun yarn super-capacitor using carbon nanotubes, which are one-dimensional carbon nanostructures, has an excellent pore structure and strength, but a scale-up process for industrialization is complicated, applicable fields are limited, its elasticity is low enough to cause breakage even at an elongation of 10%, and high manufacturing costs are required.
To address these problems, wet spun graphene or carbon nanotube (CNT) composite fibers are disclosed. These materials have improved elasticity compared to the above-described fibers, but a process of preparing mixing materials such as single-wall carbon nanotubes is complicated, use of highly purified materials is required, and the preparation process is performed under high-temperature and high-pressure conditions, requiring high manufacturing costs. In addition, a scale-up process thereof for industrialization is also complicated and difficult.
In addition, metal wires having electrical conductivity may be added to an electrode, but may act as an obstacle to application thereof to small electronic devices, such as wearable electronic fabrics and the like, due to their intrinsic stiffness and rigidity.
To address the above-described problems, a yarn-type micro-supercapacitor, manufactured by coiling a hybrid membrane obtained by coating a conductive polymer on a high-density carbon nanotube sheet, is disclosed (Korean Patent Application Registration No. 10-1214787). However, such a yarn-type micro-supercapacitor also has low elasticity and is expensive, and manufacturing processes are sensitive and complicated, and thus applicable fields are limited.
Therefore, there is a need to develop a micro-supercapacitor that has mechanical characteristics sufficient to endure various forms and deformations, excellent electrochemical characteristics, a long lifespan, and may be easily and conveniently manufactured.